Electron-Bombarded CCDs

Electron-bombarded charge-coupled devices (CCDs) are a relatively new development in which photons are detected by a photocathode in a manner similar to an image intensifier. Instructions for operation of the tutorial appear beneath the applet window.

Photons (yellow) impinging upon the surface of the photocathode liberate photoelectrons (red), which are accelerated by a high voltage gradient and impact on the back side of a CCD. Use the Gain slider to control the voltage supplied to the photocathode and, hence, the intensity or number of photoelectrons emitted by the photocathode.

The high-energy electrons that strike the CCD generate multiple charges resulting in a modest gain of a few hundred. The advantages of this device over a cooled, slow-scan CCD are the additional gain and accompanying speed; the main disadvantages are the lower quantum efficiency of the photocathode and diminished dynamic range.